Hydraulic drive for vehicles using hydraulic motors

ABSTRACT

The power input shaft of a differential pump (which has a pump output shaft, mechanical reacting means for driving the output shaft at a speed which is inverse to the quantity of fluid flowing through the pump outlet and inlet) is drivenly connected to the vehicle power plant; the pump output shaft is mechanically connected to drive one set, e.g., front, wheels; two or more positive-displacement hydraulic motors are connected to drive other, e.g., rear wheels individually; and duct and valve means are provided for interconnecting the motors either in series or in parallel with the pump inlet and outlet for varying the effective displacements of the motors. The valve means can have more than two positions: When two motors are used, three different effective displacements are achieved by connecting the motors (1) in parallel, (2) in series, (or in parallel with a change in gear ratio between each motor and its wheel); when four motors are used, two are connected to drive each wheel and the motors are connected (1) in parallel, (2) each pair of two in series with the two series-connected pairs in parallel, or (3) in series with the pump. The differential pump has a sleeve for interlocking the pump output shaft to the power input shaft, thereby stopping the pumping action. Additional positions of the valves (4) de-clutch the vehicle by interconnecting the pump outlet and inlet and (5) block flow from the pump outlet to cause equal speeds of the power input and pump output shafts.

United States Patent Greene [54] HYDRAULIC DRIVE FOR VEHICLES USING HYDRAULIC MOTORS [72] Inventor: Clarence Kirk Greene, ll55 Woodside Road, Berkeley, Calif. 94708 [22] Filed: Oct. 21, 1970 [2l] Appl. No.: 82,561

[52] US. Cl ..180/44 M, 180/66 R, 60/53 A [51] Int. Cl. ..B62d 7/00 [58] Field of Search ..180/66 R, 43 R, 43 B, 44 M; 60/53 A [56] References Cited UNITED STATES PATENTS 2,556,758 6/1951 Haynes et al, ..60/53 A 3,024,858 3/1962 Davis et a1. ..180/66 R 3,217,826 11/1965 Carter et al. ..180/43 B 3,261,421 7/ 1966 Forster et a1 ..180/66 R 3,415,334 12/1968 Vriend ..180/44 R 3,481,4l9 12/1969 Kress et al ..180/44 M 1,936,847 11/1933 Masury ..180/72 1,995,031 3/1935 Lee ..180/72 Primary Examiner-Robert G. Sheridan Attorney-Milmore & Cypher Nov. 14, 1972 [5 7] ABSTRACT The power input shaft of a differential'pump (which has a pump output shaft, mechanical reacting means for driving the output shaft at a speed which is inverse to the quantity of fluid flowing through the pump outlet and inlet) is drivenly connected to the vehicle power plant; the pump output shaft is mechanically connected to drive one set, e.g., front, wheels; two or more positive-displacementhydraulic motors are connected to drive other, e.g., rear wheels individually; and duct and valve means are provided for interconnecting the motors either in series or in parallel with the pump inlet and outlet for varying the effective displacements of the motors. The valve means can have more than two positions: When two motors are used, three different efiective displacements are achieved by connecting the motors l) in parallel, (2) in series, (or in parallel with a change in gear ratio between each motor and its wheel); when four motors are used, two are connected to drive each wheel and the motors are connected (1) in parallel, (2) each pair of two in se ries with the two series-connected pairs in parallel, or (3) in series with the pump. The difierential pump has a sleeve for interlocking the pump output shaft to the power input shaft, thereby stopping the pumping action. Additional positions of the valves (4) de-clutch the vehicle by interconnecting the pump outlet and inlet and (5) block flow from the pump outlet to cause equal speeds of the power input and pump output shafts.

9 Claims, 13 Drawing Figures PAIENTEDsuv 1 m2 3.702.642

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L RENCE KlRK GREENE Amfll 4 W HIS ATTORNEYS PATENTEIJnuv 14 m2 SHEET 2 BF 4 mm Wynn. my 3 v mm r r m N m w CLARENCE KIRK GREENE 777M 0 HIS ATTORNEYS minimum 14 um sum u or 4 mob-OE 2 54102 @OkOE INVENTOR CLARENCE KIRK GREENE WW @L HIS ATTORNEYS HYDRAULIC DRIVE FOR VEHICLES USING HYDRAULIC MOTORS The invention relates to a drive system for selfpropelled vehicles which have a power plant and a plurality of ground-engaging driving wheels wherein at least some of said wheels are driven hydraulically. In a specific aspect, the invention provides a hydraulic drive system including a plurality of fixed-displacement hydraulic motors the effective displacement of which can be varied. In another aspect, it provides a drive system which distributes the power from the power plant among driving wheels mounted on different axes, typically one disposed at the front and another at the rear of the vehicle, although this placement is not restrictive of the invention.

In an earlier patent application, Ser. No. 793,468, filed Jan. 23, 1969, (abandoned in favor of continuation-in-part application Ser. No. 106,606, now US. Pat. No. 3,680,652) there is disclosed a system for distributing the engine power among driving wheels disposed on different axes using a differential pump which is mechanically driven by the engine, the pump having a positive displacement and containing a mechanism constructed to drive an output shaft of the pump at a speed which is equal to that of the pump input shaft when the flow of hydraulic fluid from and into the pump is blocked and at progressively lower relative speeds in accordance with the rate at which the fluid is pumped. The output shaft was mechanically connected to drive the wheels on one vehicle axis and hydraulic motors, connected by ducts to the differential pump, were provided to drive wheels on another axis. Although hydraulic motors of any type could be used in that system, variable-displacement motors were often used to vary the speed of the hydraulically driven wheels in relation to the flow of hydraulic fluid.

A drawback of such a system is that, when using variable-displacement motors, it was not practicable to vary the wheel speed over as wide a range as desired,

' .since the usable range of displacements of such motors is usually not substantially greater than three to one, and such motors are very inefiicient when operated at very low displacements. Fixed-displacement motors could not be operated at different speed in relation to the flow rate of the fluid, and the speeds of the wheels driven thereby could be varied in relation to that of the pump input shaft only by the use of a variable-displacement pump.

Also, it is in many instances desirable to drive a vehicle mechanically only by one axle during normal operation and to supply additional torque to other wheels only under special conditions. For example, it is often desirable to drive a vehicle mechanically by its front wheels at all times (as through the output shaft of a differential pump) and to apply torque to the rear wheels only when accelerating, ascending a grade, or encountering conditions requiring added traction against the road. This makes it possible, for example, to enjoy the better roadability of a front-wheel drive under normal conditions and yet to avoid the need to impose sufiithe pump input shaft without having to use variable-displacement motors (although the use of variable-displacement motors in the construction of this invention is not excluded).

The present invention provides a drive system meeting the several desired characteristics previously stated. However, not all parts of the system need be employed. Thus, in one aspect, the invention provides a valving system for altering the speed of the wheels which are driven by hydraulic motors in relation to the flow of hydraulic fluid circulated by a pump (which may be but need not be a differential pump having an output shaft, and which may be of fixed displacement but need not be) without the need to use variable-displacement motors.

In summary, according to one aspect of the invention, there is provided an engine-driven pump the outlet and inlet ducts of which are connected via a valve mechanism to a plurality of hydraulic, positive-displacement motors which are mechanically coupled to drive a pair of ground-engaging wheels, the duct and valve mechanism being arranged to interconnect said motors by their intake and discharge openings either in series or in parallel. Thereby the effective displacements of the motors (i.e., the volume of fluid from the pump per revolution of the wheels) can be varied. While fixed-displacement hydraulic motors are usually employed, the use of variable-displacement motors is not excluded.

In another aspect of the invention, the said pump is a differential pump which has, in addition to the input shaft and the outlet and inlet ducts, an output shaft which is mechanically coupled to drive at least one wheel on another vehicle axis than the hydraulically driven wheels, e.g., the two wheels at the front, the speed of the said pump output shaft being inversely proportional to the rate of flow of fluid through the outlet and inlet of the pump.

The differential pump may be of any type which uses a plurality of pumping chambers, preferably of fixed displacement, such as radial or axial pistons and cylinders (as is shown in the aforesaid earlier patent application) or the spaces between the vanes of a vane pump, as described herein. Such a pump, also known as a clutch pump, has an output shaft and includes mechanical reacting means for driving the output shaft at a speed which varies, in relation to the speed of the pump input shaft, inversely with the rate at which fluid is pumped. It is evident that when the fluid can flow from the pump without any substantial opposition (as by providing a by-pass connection between the pump outlet and inlet) no torque is applied to the output shaft of the pump and the vehicle is effectively de-clutched. However, the torque on the pump output shaft is, when such flow is opposed, equal to that of the pump input shaft.

Such differential pumps can usually be operated either in their forward or reverse directions, and are driven by the vehicle engine in a manner dependent upon the location of the reversing gear and/or the transmission (which may include a reversing gear). In the embodiments to be described herein, which show a construction suitable for converting an existing frontwheel drive vehicle to use the invention, the differential pump is driven only in its forward direction, and the hydraulically driven wheels are effective only for driving the vehicle forwards. However, the reversing gear can be situated between the engine and the differential pump, (for example, as illustrated in the aforesaid earlier patent application); however, as will become apparent, in certain embodiments or operating conditions the overrunning clutch on the hydraulically driven wheels must be omitted or modified.

In certain embodiments, the serial connection of the hydraulic motors which drive wheels at opposite ends of a vehicle axis constrains the motors to rotate at a common speed. To permit one vehicle wheel to turn faster than the other, as when moving the vehicle in a turn, an overrunning clutch is provided between each wheel and the hydraulic motor or motors driving it.

While only two connections of the motors were mentioned in the broad summary of the invention, there is optionally provided at least a third operating condition of the drive for obtaining a greater variation in the ratio of the wheel speed to the flow of fluid. In one embodiment, in which there is a single, fixed-displacement motor driving each rear wheel, there is provided, in addition to the parallel and series connections of the motors, a condition in which the speed of the wheel is altered, e.g., multiplied by a planetary gear set, in relation to the motor shaft speed. In another embodiment, in which there is a plurality, e.g., two, fixed-displacement motors drivingly connected to each hydraulically driven wheel, such a planetary gear set is not required (although it can be used) and three or more different speed ratios are obtained by altering the connections of the ducts to the motors. Thus, when using two motors for each wheel, the valving is such as to: (I) place all four motors in parallel; (2) place the motors driving one wheel in parallel with those driving the other wheel but connecting each pair of motors in series; and (3) place all four motors in series.

In an optional arrangement, the hydraulic motors and the drive mechanisms associated therewith (including the overrunning clutch, when provided) are attached to the vehicle body (the term body" being used herein to include the chassis), so that they are a part of the sprung weight of the vehicle, and the wheels are driven by mechanical coupling means, such as a sprocket chain. For example, the hydraulically driven wheels can be journalled at the rear ends of resilient bars and the driven sprocket can surround the wheel brake drum at each wheel, whereby the driven sprocket can dissipate heat by radiation and/or heat can be carried off by the sprocket chain. However, in other vehicle constructions the hydraulic motors can be mounted near or coaxially with the wheels driven thereby, becoming unsprung weight.

When a differential pump is used and valve permits the vehicle to be placed in front-wheel drive (with the flow of fluid from and to the pump blocked) it is desirable to lock the pump output shaft to the pump input shaft. Thereby the pressure of fluid on the hydraulic system is reduced, e.g., brought to almost zero gauge, and the efficiency of the differential pump become 100 percent. Torque is then transmitted by the locking means instead of through the internal mechanical reacting means.

Before presenting a detailed description, it is desirable to state a few details concerning front-wheel drive (Effec. displ. of diff. pump) (Effec. displ. of hydr. motors) (Effec. displ. of diff. pump) It is evident from the foregoing that the torque to the hydraulically driven, viz., rear, wheels is multipled as the effective displacement of the hydraulic motors is increased. The parallel connection of the hydraulic motors draws the greatest quantity of fluid per revolution, thereby providing the highest effective displacement. Of course, the foregoing assumes a constant gear ratio between the motors and the wheels.

The effect of the hydraulic drive system is to draw off a portion of the power delivered by the engine to the differential pump and supply it to the rear wheels, where the power delivered is proportional to the product of the fluid pressure and the volume flow of the fluid through the motors again assuming a constant gear ratio between the motors and the wheels driven thereby.

The drive system of the invention presents a safety feature. When excessive torque is applied to the rear wheels of the usual vehicle, the front end of the vehicle tends to be raised off the roadway. In the present construction, any tendency in this direction would decrease the traction of the front wheels, eventually permitting them to spin. When at least one front wheel is free to spin the pressure of the fluid flowing from the differential pump is sharply reduced, thereby preventing the application of excessive torque to the rear wheels.

The invention is further described with the drawings forming a part hereof and showing two illustrative embodiments, wherein:

FIG. 1 is a diagrammatic plan of a motor vehicle according to a first embodiment of the invention, the valve being shown schematically and only some vehicle parts being indicated;

FIG. 2 is an elevation of one hydraulic motor and its drive mechanism, part of the mechanism appearing in section;

FIG. 3 is a section taken on the line 3-3 of FIG. 2;

FIG. 4 is a longitudinal section of a vane pump used as the differential pump, taken on the line 4-4 of FIG.

FIG. 5 is a transverse section taken on the line 5-5 of FIG. 4;

FIG. 6 is an enlarged sectional view of an O-ring;

FIG. 6 is an enlarged sectional view of an O-ring;

FIGS. 7, 8, 9 and 10 are transverse sections taken on the correspondingly numbered lines of FIG. 4;

FIG. 11 is a fragmentary longitudinal section taken on the line 11-11 of FIG. 5;

FIG. 12 is a fragmentary plan of a vehicle showing a second embodiment of the invention and corresponding to FIG. 1; and

FIG. 13 is an elevation of one set of hydraulic motors and a drive mechanism of the second embodiment.

A. FIRST EMBODIMENT l. The Overall Combination Referring to FIG. 1, the vehicle has an engine with a fly wheel 21 coupled to the input shaft of a differential pump 22 the rotatable body of which is mechanically connected to an output shaft 23. The latter drives a transmission 24, such as a speed-changing mechanism which includes a reversing gear (or may consist merely of a reversing gear). The output of the transmission 24 is connected to the input of a differential 25 which drives the front wheels 26 through horizontal axles (not shown). The front wheels are steerable by a linkage indicated at 27. The pump body, which rotates in unison with the pump output shaft 23, can be mechanically locked to the fly wheel by a sleeve 28 which is splined to the pump body and is shiftable by a lever 29, either to the free position shown or to engage the fly wheel. In the latter position all pumping action is stopped and torque is transmitted directly from the fly wheel to the pump output shaft. The fluid is transferred from the pump body through a non-rotating collector ring 30 to which an outlet duct 31 and an inlet duct 32 are connected, the latter serving to supply fluid at low pressure to the pump. These ducts are connected to a multi-way, multi-position valve 33, and 8-way, 6- position valve being illustrated.

The position of the valve is indicated by the relation of a detent bar 34 to a short line, and the first position is indicated. This valve is further connected by motor inlet ducts 35 and 36 to positive-displacement, fixeddisplacement hydraulic motors 37 and 38, and motor outlet ducts 39 and 40 extending from these motors to the valve; to pressure-responsive braking rams 41 and 42 by a duct 43; and by a duct 44 to a sump maintained under low pressure, such as the intake of an auxiliary gear pump (not shown), represented by a reservoir 45 to which fluid from the rams can flow by gravity or under a pressure less than that in the duct 31. The motors drive sprockets 46 and 47, respectively, through mechanical drive mechanisms 48 and 49 (to be described). The motors and their drive mechanisms are mounted on the vehicle body (or chassis, when present) which also carries the parts 20-24, 28-36 and 39-43, whereby these parts are sprung weights. The invention is illustrated as applied to a vehicle having its rear wheels 50 and 51 journalled on axles fast to the rear ends of resilient bars 52 and 53, the front ends of these bars being fast to the vehicle body. The brake drums 54 and 55 of these rear wheels have fixed thereto, preferably encircling them, sprockets 56 and 57, which are driven from the sprockets 46 and 47 by sprocket chains 58 aNd 59, respectively. The sprockets 56 and 57 may, for example, be shrunk onto the brake drums.

Each of the six positions of the valve 33, indicated by the position of the notched bar 34 in relation to'the single line, establishes different interconnections among the eight ducts. In the first position, shown, the ducts 31 and32 are interconnected, whereby the pump 22 pumps hydraulic fluid against a negligible flow resistance, and substantially no torque is transmitted from the fly wheel 21 to the output shaft 23; hence the vehicle is effectively de-clutched. The motors 37 and 38 are connected with the inlet of each communicating with the outlet of the same motor. Due to the overrunning clutches in the mechanisms 48 and 49, these motors do not turn when the vehicle moves forwardly, but they do turn in their reverse directions when the vehicle moves rearwardly; this causes flow through the lines 35, 36, 39 and 40 in directions opposite to those indicated by the arrows. The rams 41 and 42 are vented to the low-pressure sump 45.

When the valve is in its second position (which can be visualized by imagining the strip of six rectangles shifted one position toward the left) the motors 37 and 38 are interconnected in parallel, the pressure duct 31 supplying fluid to the motor inlet ducts 35 and 36, and the motor outlet ducts 39 and 40 delivering fluid to the pump inlet duct 32. The rams 41 and 42 are vented, as in the first valve position.

When the valve is in its third position, the motors 37 and 38 are connected in series, thereby passing a greater quantity of fluid per revolution, turning faster in relation to the flow of fluid from the pump and generating less torque than in the second valve position. Thus, the duct 31 supplies fluid to the duct 35; fluid from the duct 39 is transferred to the duct 36; and

fluid from the duct 40 is fed to the pump inlet duct 32.

The rams 41 and 42 are still vented.

When the valve is in the optional fourth position, the motors 37 and 38 are again interconnected in parallel, as in the second valve position. This position differs from the second position only in that pressure is applied to the rams 41 and 42 via the duct 43, as from the pump discharge duct 31, thereby increasing the speed of the sprockets 46 and 47 in relation to the motor shafts through a planetary gear set forming a part of the mechanisms 48 and 49, to be described.

The fifth valve position is identical to the first and is optional.

When the valve is in its sixth position, the inlet of each motor 37 or 38 is again connected to the outlet of the same motor and the rams 41 and 42 are vented. However, the ends of the ducts 31 and 32 are closed, thereby blocking the flow of fluid to and from the differential pump and causing the pump output shaft 23 to turn at the same speed and with the same torque as the fly wheel 21 (except for loss due to leakage of fluid). This loss can be reduced to zero by sliding the sleeve 28 to lock the pump body to the fly wheel and effecting a mechanical connection. The vehicle is then in front wheel drive.

The valve 33 may take any suitable form. Thus, it can be a rotary valve, settable to any of six rotary positions and having a rotating core with ports which establish the various connections shown. However, the valving may be effected by a series of two-way, two-position valves, which are selectively opened or closed by a cam or other mechanism. Since valves are known per se, no specific construction is shown.

II. The Mechanical Drives FIGS. 2 and 3 show the mechanical drive 48 on the right side, the drive 49 for the left being a mirror image of that shown. The hydraulic motor 37 may be any positive-displacement motor, preferably having a fixed displacement. While any form of hydraulic motor can be used, including vane motors, more usually it will have cylinders and pistons which are reciprocated from a swash plate or gears. The motor has an output shaft 60 to the end of which is bolted a disc 61, which is preferably splined to the output shaft. The disc is formed with a central, circular cavity 62, which carries an overrunning clutch of any suitable and desired type. In this embodiment, the clutch includes a hexagonal plate 63 having shoulders 64, balls 65 and springs 66 acting between the shoulders and the balls to wedge the latter between the disc and the plate. It is evident that the disc 61 can rotate counterclockwise (as seen in H6. 3) relatively to the plate 63, but that no relative motion in the opposite direction is possible. The plate 63 is bolted to a sun wheel or gear 67, as by countersunk screws, the gear 67 being freely rotatable on the motor shaft 60 and splined to a sleeve 68. This sleeve carries the sprocket 47, secured thereto for rotation therewith. When the rams 41 are vented, forward rotation of the motor 37, therefore, drives the sprocket 47 at the same angular speed, but the sprocket can overrun the motor forwardly.

The disc 61 carries three planetary gears 69, 70 and 71, which are freely rotatable on spindles 72 carried by the disc and mesh with the sun gear 67. An internal gear 73 meshes with the three planetary gears and has limited axial motion between a stationary friction ring 74 and the plungers 75 of the rams 41 (or 42). There may, for example, be three rams 41 hearing on each internal gear 73 at points displaced 120 apart. Each ram may include a cylinder and a piston or a sylphon bellows and be provided with spring means for retracting the plungers when the rams are vented. These plungers, when extended, push the gear 73 against the stationary ring 74 to stop the rotation of the gear. The ring 74 may be of any suitable material, such as metal, or of cork carried by a metallic ring. When cork is used, it is desirable to lubricate it, as by enclosing the entire disc 61, ring 74, gears and the rams 41 within an oil-filled housing (not shown) having a running seal about the sleeve 68. The relative sizes of the gears are preferably such as to increase the rotary speed of the sprocket when the rams 41 are pressurized to stop the rotation of the internal gear 73. Suggested diameter ratios for the gears and sprockets are given hereinafter. It may be noted that when the internal gear 73 is stopped the overrunning clutch is ineffective to transmit torque forwardly because the gear 67 rotates faster than the disc 61.

Ill. The Differential Pump Referring to FIGS. 4-11, the fly wheel 21, which is bolted to the engine output shaft 76 by cap screws 77, has bolted to it by cap screws 78 a pump input shaft 79. The latter is splined to a pump rotor 80 having an external cross section of circular shape by splines 81, and is journalled to a rotatable housing which includes an end wall 82 by a ring of ball bearings 83. The inner race of this ring is secured to the shaft by a snap-on ring and a nut 84, and the shaft is sealed to the housing by suitable seal means, represented by a bushing 85 carrying a series of seal rings 86 which are retained by a gland 87. The inner end of the shaft has radial support in a bronze or bronze-alloy bearing bushing 88 which is fixed within an end block 89 of the pump housing. The block 89 is bolted to the wall 82 by cap screws, of which only two screws 90 are shown. These screws also fix end plates 91 and 92 and an outside camming wall 93, the latter having internally an oval shape with its smallest diameter only slightly greater than that of the rotor, as appears in FIG. 5. The wall 93 is externally circular in cross section and carries a series of longitudinal splines 94, which guide the sleeve 28 for axial sliding movement but secure the sleeve against relative rotation. The end of the sleeve nearer the fly wheel is adapted to make frictional contact therewith, to stop relative rotation between the pump housing or body and the fly wheel when urged against the fly wheel by the lever 29. The latter engages the sleeve by projections fixed thereto which enter a circumferential groove 95 in the sleeve. This lever can be controlled manually, either separately or, if desired, connected to the transmission 24 or to the controller for the valve 33 to engage the fly wheel when the valve is in its sixth position.

The rotor 80 is formed with a plurality of radial (or inclined) slots, twelve slots being shown, each slot containing a radially slidable vane 96. These vanes are at all times in sliding and sealing relation to the end plates 91 and 92 and to the camming wall 93. They are urged outwardly by light springs 97 which are interposed between the inner edges of the vanes and the bottoms of the slots in the rotor, aided by the centrifugal force developed when the rotor turns with the engine and by fluid pressure acting against the inner edges of the vanes, admitted as will be described. The rotor may, for example, be of alloy steel, carburized and hardened; the vanes are preferably made of a steel containing tungsten, such as high-speed tool steel, properly hardened, as considerable heat is generated at the high rubbing speed; the camming wall or vane track 93 may be made from a carburizing grade of alloy steel and hardened; and the end plates 91 and 92 may be made from manganese or silicon bronze.

The end plate 92 is formed with a pair of diametrically oppositely located discharge ports 98 and 99, and with a pair of similarly related intake ports 100 and 101, the functional appellations being applicable when the rotor turns relatively to the housing in the direction of the arrow 102. These ports are circumferentially separated by laps which subtend angles at the rotor axis at least as great as the angular distance between successive vanes, to avoid by-passing of fluid. The plate 92 further has, also extending therethrough, a pair of ports 103 and 104 which communicate with the bases of the rotor slots to admit fluid from the pressure or discharge side of the pump. The latter ports extend substantially through the angles subtended by the discharge ports and the lap angles. The ports 98, 99, 103 and 104 are in communication via passages 105, 106, and 107 with an annular discharge groove 108, all formed in the block 89. The end plate 91 is formed with ports 109 and 1 10, which extend therethrough and communicate with the bases of the rotor slots to admit fluid from the intake side of the pump. The last-mentioned ports extend substantially through the angles subtended by the intake ports 100 and 101. These intake ports of the plate 92 are in communication via passages 111 and 112 with an annular intake groove 113, all formed in the block 89.

The passages 111 further communicate via radial passages 114 and axial passages 115, formed in the block, and axial bores 116-118 formed in the plates 91 and 92 and in the wall 93, with passages 119 formed in the wall 82 (FIG. 11) the latter communicating with the ports 109 and 110.

Optionally, the plate 91 has hollowed out regions 120 locatedoppositely to the ports 103 and 104 of the plate 92. Similarly, the plate 91 optionally has hollowed out regions 121 opposite to the ports 109 and 110 of the plate 91. The regions 120 and 121 are depressions and do not extend through the plates. They may be provided to facilitate the flow of hydraulic fluid for lubricating the ends of the rotor.

Because vane pumps are well known per se, certain conventional parts, such as circular grooves in the end plates 91 aNd 92, axial thrust bearings for the rotor, and the like, which are optionally present are not shown. It will be noted that the vane pump described is of the balanced, double-lobe type, which pumps fluid simultaneously from two diametrically opposite regions and draws fluid into two other diametrically opposite regions. However, other forms of vane pumps can be used.

A collector system of any suitable and desired form is used to transfer fluid between the rotating block 89 and a stationary part of the vehicle body or chassis. For example, it can include a ring 122 which is secured against rotation but is free to align itself with the pump axis. The block 89 is rotatably mounted within the ring 122 by rings of ball bearings 123, 124, which are retained by rings 125-127 which are, in turn, secured by cap screws 128. These bearings provide radial as well as axial relative positions. The ring 122 is formed with a pair of radial ports 129 and 130 for attachment of the discharge and intake ducts 31 and 32 respectively (FIG. I); it corresponds to the collector ring 30. These radial ports are in constant communication with the discharge and intake grooves 108 and 113, respectively. Suitable running seals are provided between the block 89 and the ring 122 to isolate the grooves from each other and from the outside, such as O-rings 131, 132 and 133, which are situated within annular grooves 134 formed in the ring 122 and located between the grooves and to each side thereof. It will be understood that the drawings are only diagrammatic, since in practice each O-ring shown would be embodied by at least two O-rings and that additional sealing means would back up the outer rings 132 and 133. In a specific embodirnent, shown in FIG. 6, each O-ring may comprise a central ring 135 of compressible material which touches the base of the groove 134 and is encased at its sides and toward the ring 122 by a wear-resistant cover 136, e.g., made of tetrafluoroethylene, known as Teflon."

The output shaft 23 is bolted to the block 89 by cap screws 137.

When the flow of hydraulic fluid through the ports 129 and 130 is blocked (as when the valve 33 is in its sixth position) no fluid is pumped and there is no relative angular motion between the shafts 79 and 23 (except for motion due to leakage); when the fluid can flow with almost no opposition (as when the valve 33 is in its first or fifth position) no torque is transmitted between these two shafts; and at other positions of the valve the rotation of the output shaft 23 in relation to the input shaft 79 is inversely proportional to the amount of fluid pumped.

It will be understood that the hydraulic system is, in practice, provided with additional elements, such as an auxiliary pump for maintaining the pump and ducts filled with fluid, a reservoir for fluid and pressure-relief valves. These, being conventional, are not shown.

IV. Dimensions and Gear Ratios Without in any way limiting the invention to specific values, the following are given to aid in the construction of the vehicle drive system. It will be understood that the dimensions and pressures may be chosen from a wide range of values, governed usually by the horsepower of the vehicle.

High-speed hydraulic motors 37 and 38 are used, operating at a pressure difference between the inlet and outlet of from one to three thousand psi., and may have a displacement of l to 3 cu. in., e.g., 1.5 cu. in. per output shaft revolution. The differential pump 22 may deliver about two-thirds of the stated volume per engine revolution, e.g., 1 cu. in., when the output shaft 23 is held stationary.

The planetary gears 69 71 may have diameters twice that of the sun gear, whereby the sprockets 46 and 47 are rotated 6 times as fast as the motor output shafts when the internal gears 73 are held stationary.

The driven sprockets 56 and 57 may have four times as many teeth as the driving sprockets 46 and 47.

V. Operation of the First Embodiment The vehicle can be placed into operation to move forwardly from a standstill either from the first or fifth position of the valve 33. Starting from the first position, by moving the valve through the 2nd through the 4th positions, the rear wheels are driven with progressively decreasing torque and increasing speed for a given speed of the engine; by going to the sixth position the vehicle is placed into front-wheel drive. The effects are:

1. When the valve 33 is in its first position, as shown, the engine is de-clutched, since the fluid flows against almost no opposition from duct 31 to duct 32. No torque is delivered to the pump output shaft 23 or to the rear wheels.

2. When the valve is in its second position, the hydraulic motors 37 and 38 are connected in parallel, thereby drawing the greatest amount of fluid and exerting the greatest torque on the rear wheels. With the size ratios given above, the rear wheels make one revolution for four revolutions of the hydraulic motors, drawing 12 cu. in. of fluid per wheel revolution. The torque delivered to the front wheels depends upon the engine torque and the setting of the transmission 24 as well as the gear ratio in the differential. Typically, the engine would turn about 14 to 18 times for each revolution of the wheels (12 revolutions to supply fluid to the motors 37 and 38 and two to six revolutions to drive the front wheels). A value of 16 engine revolutions per wheel revolution is an example. It may be noted that the output shaft 23, although rotating more slowly than the input shaft 79, exerts substantially the same torque.

3. When the valve is in its third position, the hydraulic motors 37 and 38, being connected in series, draw less fluid, e.g., 6 cu. in. per wheel revolution.

The pump output shaft 23 now rotates more rapidly in relation to the input shaft 79, still with the same torque. For example, the may make about revolutions per wheel revolution.

4. When the valve is in its fourth position, the hydraulic motors are again connected in parallel; however, the rams 41 and 42 are pressurized to stop the rotations of the internal gears 73, whereby the angular speeds of the sprockets 46 and 47 are increased, e.g., by factors of six, causing the motors to draw 2 cu. in. of fluid per wheel revolution for the ratios stated. This causes a further increase in the speed of the output shaft 23 in relation to that of the input shaft 79 and, as an example, the engine would rotate about 6 or 7 times per wheel revolution.

5. When the valve is in its fifth position, the vehicle is de-clutched, as was described for the first position.

6. When the valve is in its sixth position, no fluid is supplied to the motors 37 and 38, and the vehicle is in front-wheel drive. As an example, the engine can rotate about 4 times for each wheel revolution.

By shifting the sleeve 28 to engage the fly wheel 21 when the valve is in its sixth position the output shaft 23 can be locked mechanically to the fly wheel, whereby pumping action is stopped and pressure is relieved from the grooves 108 and 113 and the O-rings. The efficiency of the differential pump is now unity. These positions of the valve and sleeve are the most usual, since the other positions are used only for idling or when torque is applied to the rear wheels.

The overrunning clutches (parts 62 66) are important when the valve is in its third position (and the motors, being in series, operate at a common speed) to permit one wheel to rotate faster than the other, as when making a turn or due to different tire sizes on the rear wheels. These clutches are, further, operative in the sixth valve position in that they prevent rotation of the motors when the vehicle moves forwardly. However, these motors rotate backwardly when the vehicle is moved rearwardly, the fluid being passed between the two motors which are serially connected.

B. SECOND EMBODIMENT VI. The Overall Combination Referring to FIG. 12, the vehicle is constructed, from the engine forwards, as was previously described. Each rear wheel 50 and 51 is driven by a pair of hydraulic motors 138 and 139, or 140 and 141, the output shafts of each pair of motors being mechanically connected for rotation in unison and further connected to a drive mechanism 142 or 143. These drive mechanisms comprise merely an overrunning clutch (as was previously described in connection with FIGS. 2 and 3) which drives the sprocket 46 or 47, the planetary gears and rams being omitted. These sprockets drive the sprockets 56 and 57 as previously described, the rear wheels being similarly constructed and mounted.

Each hydraulic motor has an inlet duct 144, 145, 146 or 147, and an outlet duct 148, 149, 150 or 151, and these ducts, together with the ducts 31 and 32 from the differential pump, are connected to a multi-way, multiposition valve 152, a l0-way, 6-position valve being illustrated schematically in its first position, indicated by the position of the detent bar 153. When the valve is in its first or in its fifth position, the ducts 31 and 32 are interconnected, whereby the vehicle is de-clutched; each motor has its inlet duct connected to its outlet duct.

When the valve is in its second position, all four motors 138-141 are connected in parallel. In the third valve position, fluid from the duct 31 is supplied to the ducts 144 and 146, and fluid from the ducts 149 and 151 is returned to the duct 32; fluid is further transferred from the duct 148 to the duct 145, and from the duct 150 to the duct 147. In other words, the motors 138 and 139 are connected in series, as are the two motors 140 and 141, but each pair of series-connected motors is in parallel with the other.

When the valve is in its fourth position, all four motors are connected in series with the differential pump: flow is from the duct 31 to the duct 144, from duct 148 to duct 145, from duct 149 to duct 147, from duct 151 to duct 146, and from duct to the duct 32.

When the valve is in its sixth position each inlet port of each motor is again connected to the outlet port of the same motor. The ends of the ducts 31 and 32 are closed, thereby blocking all flow of fluid to and from the differential pump.

VII. The Mechanical Drives FIG. 13 shows the mechanical drive mechanism at the right side, that for the left being a mirror image of that shown. The output shaft 154 of the hydraulic motor 138 is mechanically connected to rotate with the input shaft 155. The latter is bolted by flanges 156 to the output shaft 157 of the hydraulic motor 139. The output shaft 154 is bolted to a disc 158, which may be splined to the said output shaft and is formed with a central, circular cavity 159 which contains an overrunning clutch. This clutch includes a hexagonal plate 160, surrounded by six balls 161 which are adapted to be wedged between the disc and the plate and are urged by springs, mounted as was described in connection with FIGS. 2 and 3. The balls and hexagonal plate are retained by a ring 162. Splined to the plate is a sleeve 163 which carries fixed for rotation therewith the sprocket 46 and which is freely rotatable about the motor output shaft 154.

VIII. Dimensions and Gear Ratios Without limiting the invention, the following specific values are given as suitable for one installation:

Each hydraulic motor 138 141 may have a displacement of 0.75 cu. in. of fluid per shaft revolution and operate at the pressures and with the differential pump as previously described.

The driven sprockets 56 and 57 may have 4 times as many teeth as the driving sprockets 46 and 47.

While, with the valve connections shown, all four motors should have the same displacement, it is evident that with other valve connections the two motors at each side of the vehicle may have different displacements.

IX. Operation of the Second Embodiment The vehicle can be placed into operation from a standstill as was described for the first embodiment, and the progression of vehicle speeds varies with the positions of the valve 152 as was described for the valve 33, with the following differences:

1. When the valve 152 is in its second position, the

four hydraulic motors are connected in parallel and draw a total of twelve cu. in. of hydraulic fluid per revolution of the rear wheels 50 and 51. Therefore the ratio of engine revolutions to wheel revolutions is the same as in the first embodiment.

. When the valve is in its third position, each pair of series-connected motors draws three cu. in. of fluid per wheel revolution, all four motors therefore drawing six cu. in. of fluid. Hence the ratio of engine revolutions to wheel revolutions is the same as in the first embodiment.

3. When the valve is in its fourth position, all four motors are connected in series, thereby drawing three cu. in. of fluid per wheel revolution. Therefore the engine turns about 7 or 8 times for each turn of the wheels. It may be noted that when all four motors are connected in series the overrunning clutches 158 161 permits the rear wheels 50 and 51 to operate at different speeds although the motor shafts turn at the same speed.

I claim:

1. In a self-propelled vehicle having a power plant and a plurality of ground-engaging elements which include driving wheels, a hydraulic drive system which comprises:

a. a pump having a power input shaft drivenly connected to said power plant, a high-pressure fluid outlet, and a fluid inlet,

. at least one pair of positivedisplacement hydraulic motors each having intake and discharge openings and a motor output shaft.

c. duct and valve means for varying the effective displacements of said motors by connecting the intake and discharge openings thereof selectively in series or in parallel with the inlet and outlet of the Pump,

d. a variable gear ratio mechanism interconnected between each said motor output shaft and a wheel driven by said shaft, said mechanisms having means for selectively placing the mechanisms into a first or a second condition inwhich the wheels are driven at different speeds in relation to the speeds of the motor output shafts, and

e. said duct and valve means includes actuating means for placing said variable gear ratio mechanisms into the first condition when the motors have one displacement and placing said variable gear ratio mechanisms into the second condition when the motor displacements are different from said one displacement.

. The vehicle according to claim 1 wherein:

. each of said variable gear ratio mechanisms includes a planetary gear set having an input gear drivenly connected to the motor output shaft, an output gear drivingly connected to the wheel, and a floating gear which is stationary in one of said conditions and is free to rotate in the other condition, and

. the means for selectively placing the variable gear ratio mechanism into one or the other of said conditions includes:

l. friction means for stopping the rotation of the floating gear, and

2. fluid pressure-responsive means connected to said duct and valve means for making said friction means selectively operative or inoperative.

3. The vehicle according to claim 1 wherein:

a. said duct and valve means includes three positions of the valve in which the said motors are connected, respectively, in parallel, in series, and in parallel with the pump, and

b. said duct and valve means includes actuating means for placing said variable gear ratio mechanisms into the first condition while placing said motors into one of said parallel connections, and for placing said variable gear ratio mechanism into the second condition while placing said motors into series connection and into the other of said parallel connections.

4. In a self-propelled vehicle having a power plant and a plurality of ground-engaging elements which include driving wheels situated on longitudinally displaced transverse axes, a combined mechanical and hydraulic drive system which comprises:

. a. a pair of driving wheels on one transverse vehicle axis, and at least one additional driving wheel situated on a different transverse vehicle axis,

b. a differential pump having a power input shaft drivenly connected to said power plant, a highpressure fluid outlet, a fluid inlet, a pump output shaft, and mechanical reacting means for driving said pump output shaft at a speed which varies, in relation to the speed of said power input shaft, inversely with the quantity of fluid flowing through said outlet and inlet of the pump,

. mechanical means for drivingly connecting said pump output shaft to the said additional driving wheel,

. at least one pair of positive-displacement hydraulic motors each having intake and discharge openings and a motor output shaft which is drivingly connected to a separate driving wheel on said one vehicle axis, and

. duct and valve means for varying the effective displacements of said motors by connecting the intake and discharge openings thereof selectively in series or in parallel with the inlet and outlet of the pump.

5. The vehicle according to claim 4 wherein said differential pump is a fixed-displacement pump.

6. The vehicle according to claim 4 wherein said duct and valve means includes means for blocking the flow of fluid from said output of the pump.

7. The vehicle according to claim 6 wherein said duct and valve means includes means for interconnecting the discharge openings of at least two of said motors respectively to intake openings of two separate motors when the flow of fluid from the outlet of pump is blocked.

8. The vehicle according to claim 4 which includes means for mechanically preventing relative rotation between the power input shaft and the pump output shaft.

9. The vehicle according to claim 4 wherein said duct and valve means includes valve means having at least four positions in which, respectively:

a. said outlet and inlet of the differential pump are interconnected for the direct flow of fluid against negligible flow resistance,

b. at least two hydraulic motors are connected in parallel with the pump,

c. at least said two hydraulic motors are connected in series with the pump, and 

1. In a self-propelled vehicle having a power plant and a plurality of ground-engaging elements which include driving wheels, a hydraulic drive system which comprises: a. a pump having a power input shaft drivenly connected to said power plant, a high-pressure fluid outlet, and a fluid inlet, b. at least one pair of positive-displacement hydraulic motors each having intake and discharge openings and a motor output shaft. c. duct and valve means for varying the effective displacements of said motors by connecting the intake and discharge openings thereof selectively in series or in parallel with the inlet and outlet of the pump, d. a variable gear ratio mechanism interconnected between each said motor output shaft and a wheel driven by said shaft, said mechanisms having means for selectively placing the mechanisms into a first or a second condition in which the wheels are driven at different speeds in relation to the speeds of the motor output shafts, and e. said duct and valve means includes actuating means for placing said variable gear ratio mechanisms into the first condition when the motors have one displacement and placing said variable gear ratio mechanisms into the second condition when the motor displacements are different from said one displacement.
 2. fluid pressure-responsive means connected to said duct and valve means for making said friction means selectively operative or inoperative.
 2. The vehicle according to claim 1 wherein: a. each of said variable gear ratio mechanisms includes a planetary gear set having an input gear drivenly connected to the motor output shaft, an output gear drivingly connected to the wheel, and a floating gear which is stationary in one of said conditions and is free to rotate in the other condition, and b. the means for selectively placing the variable gear ratio mechanism into one or the other of said conditions includes:
 3. The vehicle according to claim 1 wherein: a. said duct and valve means includes three positions of the valve in which the said motors are connected, respectively, in parallel, in series, and in parallel with the pump, and b. said duct and valve means includes actuating means for placing said variable gear ratio mechanisms into the first condition while placing said motors into one of said parallel connections, and for placing said variable gear ratio mechanism into the second condition while placing said motors into series connection and into the other of said parallel connections.
 4. In a self-propelled vehicle having a power plant and a plurality of ground-engaging elements which include driving wheels situated on longitudinally displaced transverse axes, a combined mechanical and hydraulic drive system which comprises: a. a pair of driving wheels on one transverse vehicle axis, and at least one additional driving wheel situated on a different transverse vehicle axis, b. a differential pump having a power input shaft drivenly connected to said power plant, a high-pressure fluid outlet, a fluid inlet, a pump output shaft, and mechanical reacting means for driving said pump output shaft at a speed which varies, in relation to the speed of said power input shaft, inversely with the quantity of fluid flowing through said outlet and inlet of the pump, c. mechanical means for drivingly connecting said pump output shaft to the said additional driving wheel, d. at least one pair of positive-displacement hydraulic motors each having intake and discharge openings and a motor output shaft which is drivingly connected to a separate driving wheel on said one vehicle axis, and e. duct and valve means for varying the effective displacements of said motors by connecting the intake and discharge openings thereof selectively in series or in parallel with the inlet and outlet of the pump.
 5. The vehicle according to claim 4 wherein said differential pump is a fixed-displacement pump.
 6. The vehicle according to claim 4 wherein said duct and valve means includes means for blocking the flow of fluid from said output of the pump.
 7. The vehicle according to claim 6 wherein said duct and valve means includes means for interconnecting the discharge openings of at least two of said motors respectively to intake openings of two separate motors when the flow of fluid from the outlet of pump is blocked.
 8. The vehicle according to claim 4 which includes means for mechanically preventing relative rotation between the power input shaft and the pump output shaft.
 9. The vehicle according to claim 4 wherein said duct and valve means includes valve means having at least four positions in which, respectively: a. said outlet and inlet of the differential pump are interconnected for the direct flow of fluid against negligible flow resistance, b. at least two hydraulic motors are connected in parallel with the pump, c. at least said two hydraulic motors are connected in series with the pump, and d. the flow of fluid from the outlet of the pump is blocked, the said series and parallel connections of the motors being through their intake and discharge openings. 